This invention relates to electronic locking devices. In particular the invention relates to a simple device and method for locking drawers, doors or other closable compartments in furniture such as office desks. Modern telephones which are connected to electronic switching exchanges produce a tone whose frequency depends upon the number dialed. When dialing a number in this way a series of tones are supplied along the telephone line and the tones are reproduced by the ear piece of the telephone. The frequencies of the tones produced are of known internationally accepted values.